1. Field of the Invention
The present invention relates to a multiplex resolver which enables continuous monitoring of variation and imbalance of output signals, as well as reliable provision of output signals irrespective of occurrence of anomaly, such as wire breaking, in a portion of output windings and excitation windings. More particularly, the present invention relates to a multiplex resolver which includes m integrated resolver units (m is an integer not less than 2) and which has a reduced overall size as measured in the axial direction.
2. Related Art
Conventionally, in the case of a machine or apparatus in which a safety problem arises when output signals of a resolver vary or are lost, redundancy imparting means is provided in order to secure safety. Specifically, two identical resolvers are provided, and a plurality of signals output from the resolvers are monitored and compared so as to judge whether or not an anomaly has occurred. When one of the resolvers is broken and its output signals are lost, operation is continued on the basis of output signals of the other, normal resolver. Such redundancy imparting means is disclosed as a prior art technique in Japanese Patent Application Laid-Open No. 2000-18968.
The known redundancy imparting means is described as having the following drawback. Since windings wound on a stator project to the opposite sides of stator magnetic poles, a resultant resolver axially projects at least by an amount corresponding to the projecting amount of the windings, which makes it difficult to reduce, for miniaturization, the size as measured along the axial direction.
FIGS. 1A to 1D show a structure of a conventional resolver including two resolver units A and B. FIG. 1A shows the stator structure of the resolver unit A. Magnetic poles project from a stator yoke 100 at intervals of 90°, starting from a position of 12 o'clock serving as a reference position (0°). Windings 101, 102, 103, and 104 are wound clockwise around the respective magnetic poles. The windings consist of an excitation winding, and sin (sine) and cos (cosine) windings having a phase difference of 90° therebetween.
FIG. 1B shows the stator structure of the resolver unit B. Magnetic poles project from a stator yoke 109 at intervals of 90°, starting from a position of 12 o'clock serving as a reference position (0°). Windings 105, 106, 107, and 108 are wound clockwise around the respective magnetic poles.
When the resolver units A and B are juxtaposed, they provide an external shape of FIG. 1C when viewed from the front. When the resolver units A and B are viewed from the side, as shown in FIG. 1D, the windings project from the stator yokes 100 and 109. Therefore, the two resolver units are disposed with a separation corresponding to the projection amounts of the windings.
In order to solve this drawback, in the resolver disclosed in the patent publication, coils are wound on the stator in a divided manner to avoid overlapping of coil areas.
However, the stator of the resolver disclosed in the patent publication is a single ring-like stator having an overall annular shape, and does not have a commonly used structure in which stator magnetic poles project toward the center from an annular stator yoke. Therefore, the patent publication neither discloses nor suggests application of the above-described redundancy imparting means to ordinary stators. Further, the publication neither discloses nor suggests the specific configuration of windings.